Path calculation systems are proposed and put into practical use for calculating the optimum path (the shortest path, for example) from a node as the start node to another node as the end node on an SDH (Synchronous Digital Hierarchy) network.
For example, the path calculation system described in the Patent Document 1 specified hereinbelow first establishes network topology information in a database including information of the nodes which constitute the SDH network, and information of the links which connect the nodes. Next, the path calculation system generates a topology data for actual path calculation from the network topology information maintained in the database. In particular, it arranges the nodes into lines and columns so as to generate the topological lines and columns on which a value has been assigned to each element of the lines and columns to indicate whether or not there is a link including an unused time slot between the corresponding nodes. Then, the path calculation system utilizes an ordinary path calculation algorithm such as Dijkstra's algorithm and the like to calculate the shortest path based on the topology data for between the start node and the end node on the request of path calculation from the operator.    [Patent Document 1] JP 2000-232472 A
However, with the related technology described hereinabove, there is a problem that it is impossible to calculate optimum paths for an entire network allowing coexistence of PDH (Plesiochronous Digital Hierarchy) network and SDH network as the object. The reason is that the conception of time slot does not exist in the PDH network, etc., and thereby the topology data for path calculation are different between a PDH network and an SDH network.